G70 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



of note thai the smallest species {Sciurus hudsonius) is the most northern, 

 and that the nexl smallesl [Sciurus eestuans) is the most southern, both 

 occurring on the extreme boundaries of the habitat of the group. These 

 ogain, in respect to the development of the tail, arc the least Sciurine; the 

 long, lull, bushy, distichous tail, so characteristic a feature of the Sciuri as 

 distinguishing them from their allies, being in these two species very much 

 shorter and narrower than in any of the others. In passing southward, we 

 meet, next alter 8. hudsonius, with S. carolinensis, a species again below the 

 average in size, with the tail only moderately developed, although there are 

 some Mexican and Central American species equally small. The largest 

 species, as well as the greatest number, and those with the largest tails, are 

 Mexican ; Western and Southern Mexico being apparently the centre of devel- 

 opment, or metropolis of* the group, as respects the two Americas. None are 

 thus far known from any of the intertropical islands. 



As already observed, the American Sciuri form a group so homogeneous 

 as not to be readily subdivisible. Taking, however, the relative length of the 

 tail, and the number and character of the upper premolars, as a basis, with such 

 other features as are most readily available, the species and subspecies may 

 be conveniently (and somewhat naturally) grouped as follows: — 



SYNOPSIS OF THE SPECIES AND SUBSPECIES OF AMERICAN SCIURI. 



I. Tail very short ami narrow, the caudal vertebrae alone about two-thirds as long as tbe head and body ; 

 tail to end of hairs about one-seventh shorter than the head and body ; premolars f , the 

 first very small and often deciduous ; a narrow, black, lateral line ; size small. One 

 species with four subspecies : 

 1. Above grayish, mixed with yellowish or reddish, anuulated with dusky, often with a strong 

 wash of ferruginous along the middle of the back ; below generally white, sometimes 

 narrowly annotated with black; in one subspecies fulvous below. Hah.— Northern half 



of North America S. HUDSONIUS. 



o. Above yellowish-gray, varied with black, with generally the middle of the back strongly 

 washed with ferruginous; upper surface of the tail with the hairs rusty at the base and 

 reddish-tipped, with a broad snbterminal bar of black. Hab.— Northern North America 

 east of the Rocky Mountains and northwestward to Alaska var. hudsonius. 



b. Above varied with black and yellowish-rusty ; upper surface of the tail with the bairs gray 



at the base and gray-tipped, with a broad snbterminal bar of black. Bab — Central portion 

 of the Rocky Mountains, and thence westward to the Sierra Nevadas var. fremonii. 



c. Above dusky, strongly varied with reddish ; upper surface of the tail with the hairs dark 



reddish-brown at the base, tipped with reddish, and with a very broad subterminal 

 bar of black, sometimes occupying the whole of the terminal third. Hab. — Rocky 

 Mountains between latitude 43° and 52°, and thence westward to the Cascade 

 Range .var. richardsoni. 



d. Above as in the preceding (var. richardsoni) ; tail with less black; beneath more or h ss 



strongly tinged with fulvous or rufous. Hub. — Pacific-coast region from Northern Cali- 

 fornia to Siika var. aougJatai. 



